A fuel cell is a device which converts chemical energy released during the process in which hydrogen reacts with oxygen to produce water, into electrical energy. The basic principle is equivalent to a reverse reaction of an electrolysis reaction. Fuels (H2 and CO etc.) and an oxidant (O2) are ionized into ions on a cathode and an anode of the cell by means of action of the oxidant, and forms a voltage between the negative electrode and the positive electrode by virtue of transfer ability of the ions between the electrodes through dielectric between these two electrodes. When a circuit is formed by the electrodes and an external load, it is possible to supply power outwardly.
There are many types of fuel cells, according to different applied electrolytes, mainly including a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC) and a proton exchange membrane fuel cell (PEMFC) and the like.
The fuel cell has advantages such as non-pollution, high efficiency, wide application, noise-free and continuous operation. Its power generation efficiency can reach equal to or more than 40%, and the efficiency of co-generation of heat and power also can be equal to or more than 80%. Most of the fuel cells are in the stage of research and development, although the technology like the phosphoric acid fuel cell (PAFC) is matured and already available on the market, they are still rather expensive. In view of the unique advantages of the fuel cells, they will certainly play an increasingly important role in the future gas heating industry with the advancement of commercialization process related to this technology.